RHS 300×100×8 vs CF RHS 300×100×8
RHS 300×100×8 is an RHS Hot-finished section from the UK Blue Book (SCI P363); CF RHS 300×100×8 is the closest equivalent in the UK Blue Book (SCI P363). RHS 300×100×8 carries more bending: 546 cm³ of plastic modulus against 523 cm³, 4.4% more. CF RHS 300×100×8 is the lighter of the two at 46.5 kg/m against 47.7 kg/m, a saving of 2.6% on steel weight. Both are about 300 mm deep, so either fits the same construction zone.
| Property | RHS 300×100×8 RHS Hot-finished | CF RHS 300×100×8 RHS Cold-formed | Difference |
|---|---|---|---|
| Mass | 47.7 kg/m | 46.5 kg/m | +2.6% |
| Depth | 300 mm | 300 mm | same |
| Width | 100 mm | 100 mm | same |
| Web thickness | 0 mm | 0 mm | same |
| Flange thickness | 0 mm | 0 mm | same |
| Area | 60.8 cm² | 59.2 cm² | +2.7% |
| Second moment, major (Iy) | 6,310 cm⁴ | 5,980 cm⁴ | +5.5% |
| Plastic modulus, major (Wpl,y) | 546 cm³ | 523 cm³ | +4.4% |
| Elastic modulus, major (Wel,y) | 420 cm³ | 399 cm³ | +5.3% |
| Second moment, minor (Iz) | 1,080 cm⁴ | 1,050 cm⁴ | +2.9% |
| Plastic modulus, minor (Wpl,z) | 245 cm³ | 238 cm³ | +2.9% |
| Radius of gyration, minor (iz) | 4.21 cm | 4.2 cm | +0.2% |
| Torsion constant (It) | 3,070 cm⁴ | 3,080 cm⁴ | -0.3% |
RHS 300×100×8 to BS EN 10210-2:2006; CF RHS 300×100×8 to BS EN 10219-2:2006. Difference is expressed relative to CF RHS 300×100×8.
How to choose between them
On stiffness, RHS 300×100×8 has the larger second moment of area: 6,310 cm⁴ against 5,980 cm⁴, a difference of 5.5%. This matters more often than the strength comparison, because on normal floor spans deflection rather than bending capacity sets the beam size - so if the two are close on modulus but apart on inertia, the stiffer one is usually the better answer even when it is not the stronger one.
Measured as bending capacity per kilogram, the two are equally efficient (11.4 against 11.2 cm³ per kg/m), so on a pure steel-tonnage basis there is nothing to choose between them. The decision comes down to availability, connection detailing and what the rest of the frame uses.
In short, RHS 300×100×8 is the stronger section and CF RHS 300×100×8 is the lighter one; where those are the same section, it is the clear choice, and where they are not, decide on whether your design is governed by capacity or by tonnage.